Aircraft propulsion assembly



Feb. 11, 1941.

F. NEUGEBAUER 2,231,292

AIRCRAFT PROPULS ION AS SEMBLY Filed May 20, 1957 lave/Ital.-

Patented Feb. 11, 1941 UNITED STATES 2,231,292 I AIRCRAFT raororsros ASSEMBLY Franz Neugebauer, Dessau-Alten, Germany, as-

slgnor to Junkers Flugzeug-und-Motorenwerke Aktiengeselischaft, Dessau, Germany Application May 20, 1937, Serial No. 143,707 In Germany May 22, 1936 6 Claims.

My invention relates to internal combustion engines and more especially to the charging of aircraft engines, with compressed air.

It has been proposed to provide aircraft engines with a charging pump which compresses the air or the mixture of fuel and air, to be delivered to the cylinders of the engine, before discharging it into the cylinders, so that the pressure of the charge exceeds the atmospheric pressure. This is done in order to fully or partly compensate for the drop of output caused by a reduction of the density of the air at high altitudes. During the pre-compression of. the combustion air in the charging pump the temperature of the air will rise owing-partly to the compression per se and partly to-the losses of flow which are transformed into heat. This increase of temperature AT substantially depends on the working speed of the charging pump, that is, in a piston pump, from the number of strokes per time unit, and in a centrifugal pump from the speed according to the following formula:

AT=Cn in which n is the number of strokes per time unit. or the speed of the pump, C being a constant depending on the design and other properties of the charging pump.

If the charging pump operates at a constant working speed at all altitudes, the increase of temperature imparted to the combustion air during its pre-compression in the pump will remain constant. The initial temperature. of the charge of a cylinder of an engine must not exceed a predetermined upper limit, since other- ,wise the temperature in the engine would rise to a too high level. At low altitudes the temperatureof the ambient air is relatively high so that, ii the charging pump is allowed to operate at low altitudes, the temperature of the charge may rise above the admissible amount. Thus the charging pump should not be started before the altitude is reached at which the temperature of the pre-compressed air amounts to the admissible maximum value. At high altitudes the temperature of the ambient air is 'low, so that the temperature of the compressed charge will be correspondingly reduced and may be considerably lower than the admissible upper limit. Thus in such cases the engine might operate with still higher compressed air without reaching an inadmissible temperature. Of this possibility, however, advantage cannot be taken if a charging pump operating at a constant speed is used.

It has further been proposed to drive the charging pump at a variable speed in such manner that the pressure of the charge before entering the engine is the same at all altitudes. In that case the rate of'compression and accordingly the temperature of the pie-compressed charge will rise at increasing altitudes first slowly and then at an increasing rate. In consequence thereof the temperature of the charge will be lower at low altitudes and higher at high altitudes than admissible in regard to the engine. Thus in this case the capacity of the engine is not fully utilized at low altitudes whereas at high altitudes the engine is subject to an excessive temperature unless the charge is cooled durin ire-compression.

It has also been proposed to hold the temperature of the compressed. charge to be delivered to the engine at least approximately constant at a value suitable for the operation of the engine, this being accomplished by using a charging pump of variable operating speed which is adjusted insuch manner that the desired temperature of the charge is obtained.

If, as is usual, the charging pump is driven from the aircraft engine, a change speed gear will as a rule be provided between the engine and th pwnp so that the speed of the pump may be adjusted within the wide limits required, the change speed gear being adjustable stepswise or continually. Difllculties, however, arise if such change speed gear is to be operated in dependency from a temperature. Besides such gears are complicated and heavy in weight.

It is an object of my invention to maintain the temperature of the charge in aircraft engines, to which a pre-compressed charge is delivered by means of a pump driven by the engine, at least approximately constant by controlling the operating speed of the charging pump without providing a change speed gear, the gear ratio between the engine and the charging pump being invariable. I

Another object oi. my invention is to vary the speed of a supercharged aircraft engine by varying the pitch of a propeller driven by said' engine in response to changes in the temperature of the gases of the intake manifold of the engine.

Generally these objects of the invention are obtained by making the pitch regulating mechanism of an aircraft propeller controllable in response to changes in a temperature sensitive member located in the intake manifold of an engine having a supercharger directly geared thereto. The temperature sensitive member is responsive to variations from a fixed temperature which is chosen as the maximum temperature permissible for the intake gases without endangering the engine. When this temperature is exceeded, the pitch changing mechanism for the propeller is operated by the temperature sensitive member to increase the pitch of the propeller blades, and thus to slow the engine and supercharger, whereby the temperature of the intake gases is diminished, Conversely, if the temperature of the gas becomes less than the allowable value, the pitch changing mechanism is automatically operated to reduce the propeller pitch and thus to increase the engine and supercharger speed. Again, the device will function to regulate the speed of the engine when the temperature changes without an appreciable change in pressure, as for example when an aircraft files at a constant altitude from a cold to a warm region, and conversely.

Since, as a rule, the temperature of the charge will vary only at considerable changes of altitude of the craft, an adjustment of the propeller will be necessary only at such considerable changes.

In the drawing aifixed to this specification and forming part thereof an embodiment of'my invention is illustrated diagrammatically by way of example, the drawing being a side elevation,v partly in section, of the engine, the propeller and the charging pump.

- Referring to the drawing, 20 is the driving engine of an aircraft, which drives the propeller 3 by means of a speed reducing gear comprising the gears I and 2. The engine drives the charging pump 30 by means of gears 4, 5, the ratio of which is invariable. The blades of the propeller 3 may be adjusted during operation by rocking them about their longitudinal axes. In order to accomplish this, each blade is provided with a gear, the gear of the upper blade being marked 6, that of the lower blade 1. The gears 6 and l are engaged by racks 8 and 9, respectively, which are connected to a piston ll bymeans of a cross beam ID. The piston II is axially displaceable within a cylindrical chamber provided in the hub member l2, the chamber being subdivided by the piston into two compartments l1 and 18, which are connected to the casing l5 or to-a slide valve l6 by conduits l3 and I4 comprising stationary portions as well as portions rotating together with the propeller. flow of pressure liquid to and from the compartments l1, l8 arranged on opposite sides of the piston l I. The slide valve is controlled by means of an aneroid-like diaphragm 33 associated with a temperature-responsive member 32 arranged in the conduit 3| connecting the charging pump 30 to the en e 20. The pressure liquid required for the operation of the device is supplied by a pump 35 driven by the engine.

The operation of this device is as follows:

Temperature sensitive device 32 consists, for example, of a closed metal cylinder connected by a pipe to bellows 33. The bellows, pipe, and cylinder are filled with any expansible medium such as gas or fluid. Upon a temperature change in manifold 3|, the bellows will either expand or contract, and therewith move piston It to which it is connected.

If the temperature of the charging air increases above the admissible limit, the liquid placed under pressure by the pump 35 will be brought to act on the piston II by means of the temperature-responsive controlling means 32, 33 and the slide valve l5, IS in such manner, that the-propeller blades are adjusted so as to in- The slide valve I6 controls the crease the pitch. Thus the .resistance of the propeller will rise and the speeds of the engine 20 and of the charging pump 30 driven by the engine will decrease correspondingly, thus compensating the increase of temperature of the charge. If, on the other hand. the temperature of the charging air drops below the predetermined value, the blades'of the-propeller 3 will be ad- Justed in opposite sense, the pitch of the blades being reduced so that the resistance of the propeller drops and the speeds of the engine 20 and the charging pump 30 are increased until the temperature of the charge again reaches its initial value.'

. I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

I claim;

1. In an aircraft engine having a variable pitch propeller and a supercharger driven directly by and in fixed ratio to said engine, means for conducting compressed air from said supercharger to said engine, means for continuously measuring the temperature only of said compressed ai r,-and means for varying the pitch of said propeller to reduce the pitch and thereby increase the speed of the engine and supercharger in response to a decrease in the temperature of the compressed air as determined by said measuringan'd conversely to increase said pitch to decrease the engine speed on an increase of said temperature.

2. In an aircraft engine having a variable pitch propeller and a supercharger driven directly by and in fixed ratio'to said engine, means for measuring the temperature of air supplied from said supercharger to said engine, and means responsive only to the temperature of said air for reducing the pitch of said blades and thereby increasing said engine speed in response to a decrease in the temperature of said air, and conversely to increase said pitch to decrease said speed in response to an increase of said temperature.

3. In an aircraft engine having a variable pitch propeller and a supercharger driven directly by and in fixed ratio to said engine, means for conducting compressed air from said supercharger to said engine, hydraulic means for changing the pitch of said propellenand valve means responsive only to the temperature 01 the'air insaid propeller to reduce charger upon a rise of temperature in said conducting means and to reduce the pitch of said propeller to increase the speed of said supercharger upon a lowering of temperature in said conducting means.

4. In combination, a devicefor maintaining at a substantially constant temperature the super-- charged air entering the cylinders 01' an engine having avariable pitch propeller, and a supercharger directly driven said engine, said device comprising means responsive to changes in temperature only of the supercharged air, and means actuated by said responsive means for increasing and decreasing by and in fixed ratio to conducting means for automatically operating 1 said hydraulic means to increase the pitch of said the speed of said super-J said engine, a manifold for c'ondu'ctins compressed air from saidsupercharger to said en- 10 said valve in response to movements of said bellows to increase or decrease the pitch of said blades as determined by a rise or fall, respectively, of the temperature only in said manifold upon said device.

6. In an aircraft engine having a supercharger,

an air intake manifold connected to said supercharger, a variable pitch propeller, a hydraulic pump, and lead and return conduits connecting said pumpto said propeller: a cylinder connecting said conduits intermediate said pump and propeller, piston means movably mounted in said cylinder for reversibly interconnecting said lead and return conduits, a temperaturesensitive device in said manifold, a bellows, means connecting said device and bellows for expanding or contracting said bellows in response to changes in said device upon temperature variations in said in manifold, and a member connecting said piston means to said bellows whereby said piston means interconnects said conduits to increase or-decrease the pitch of said propeller in response to movements of said bellows upon, respectively, a Is rise or fall in the temperature in said manifold. FRANZ NEUGEBAUER. 

